Turning Device for Turning Over Sheets in a Printing Machine

ABSTRACT

The invention relates to a turning device ( 1 ) for transporting and turning over sheets ( 2 ) of printing material in a printing machine, preferably an electrophotographic printing machine, said device comprising at least two belts ( 7, 8 ), which, in particular, consist essentially of a plastic material, each of said belts being deflected as closed loops over respectively at least two deflecting elements ( 22, 23 ) and being crossed in order to turn over the respective sheet by approximately 180 degrees about its axis pointing in transport direction, in which process said sheet is held by clamping and frictional engagement between abutting segments ( 7′, 8 ′) of the tensioned belt, whereby at least one of the belts ( 7, 8 ), preferably each belt, is configured in a non-elastic manner, specifically reinforced, and that, in order to tension this belt, a tensioning device is provided.

The invention relates to a turning device for transporting and turningover sheets of printing material in a printing machine, preferably anelectrophotographic printing machine, said device comprising at leasttwo belts, which, in particular, consist essentially of a plasticmaterial, each of said belts being deflected as closed loops overrespectively at least two deflecting elements and being crossed in orderto turn over the respective sheet by approximately 180 degrees about itsaxis pointing in transport direction, in which process said sheet isheld by clamping and frictional engagement between abutting segments ofthe tensioned belt.

Turning devices of the aforementioned type are known from documents DE100 23 151 A1 and DE 100 59 913 A1, reference being made herewith totheir entire content.

For the known turning devices, the belts are tensioned in that theinherent tension of elastic belts is utilized. With respect to saidbelts' inherent elasticity and/or their coefficient of friction, thesebelts may essentially behave like rubber. However, over time, thesebelts are subject to fatigue and become loose and age overall, which,over time, impairs the transport and turning of the sheets.

Therefore, the object of the invention is to design and carry out thetransport and turning of the sheets more safely and more reliably, andin an overall more stable manner.

In accordance with the invention, this object is achieved in that atleast one of the belts, preferably each belt, is configured in anon-elastic manner, specifically rein-forced, and that, in order totension this belt, a tensioning device is provided. Therefore, inaccordance with the invention, the inherent tension due to theelasticity of the belts used is not available. In particular, to allowthe belt to continue to exhibit rubber-like behavior on the outside asfar as its coefficient of friction is concerned, the inventive belt isinstead preferably reinforced to make it non-elastic, this potentiallybeing achieved by various measures, for example, by inserting a core.However, it is also possible in accordance with the invention to use ajacket and/or a changed composition of the plastic material that isbeing used.

In accordance with the invention, tensioning devices, i.e., preferably aseparate tensioning device for each belt, are provided for tensioning orfor better tightening the belts. If needed, such a tensioning device canbe readjusted, while the lost inherent tension of a belt cannot berestored. As a result of the inventive reinforcement of the belt, saidbelt can become stiffer, and the transport can become more reliable andmore stable.

A modification of the invention provides that the tensioning devicecomprises a deflecting element which deflects or bends the belt.Preferably, however not necessarily, this is an additional deflectingelement provided in addition to the minimum of two deflecting elements,preferably deflecting rollers, which determine the course of the beltloops. Such an additional deflecting element can be adjusted in order tocontrol the desired tension, without changing the actual or main courseand the alignment of the belts. This deflecting element, preferably aroller, can preferably be moved in a direction approximately transverseto the belt travel outside the belt segment holding the sheet, and in sodoing, deflects a belt segment more or less severely out of its linearcourse and, in so doing, tightens the belt direction or the beltrotation. In this sense, it is probably better to speak of a tighteningdevice rather than of a tensioning device.

Preferably, the deflecting element is (constantly) subjected to a forceof a spring in the tensioning direction, for example, a helical spring.

In a modification of the invention, a particularly accurately adjustablebelt tensioning or belt tightening is possible in that the belt isdeflected essentially in S-form over two deflecting elements in theregion of a tensioning device, one of said deflecting elementspreferably being associated with the actual tensioning device and beingmovable subject to a spring force. One embodiment, which could result inadditional inventive features, without, however, restricting the scopeof the invention thereto, is shown by the drawings.

They show in

FIG. 1 a perspective view of a turning device of this type as disclosedby prior art, and

FIG. 2 a side elevation of a turning device in accordance with theinvention.

FIG. 1 shows an embodiment of a turning device 1 in accordance withprior art disclosed by DE 100 59 913 A1.

A sheet 2, in particular of a printing material, is transported to theright through the turning device 1 as shown by the illustration. Thetransport and turning are achieved by means of two belts 7, 8, which arearranged in such a manner that two belt segments 7′ and 8′ extend intransport direction and, in so doing, clamp the sheet 2 between them fortransport. In this arrangement, the belts 7, 8 are set at an angle orcrossed in such a manner that, upstream of a crossing region 10, thebelt segment 7′ is on top and the belt segment 8′ is on the bottom, andthat, downstream of the crossing region 10, the belt segment 8′ is ontop and the belt segment 7′ is on the bottom. As a result of thiscrossing of the belts 7, 8, the sheet 2 held between the belt segments7′, 8′ is flipped by 180 degrees about its axis pointing in transportdirection, so that, after the turn-over, the two outer edges 16, 16′ areinterchanged, and the former underside is now on top. The advantage ofsuch a turning device, in contrast with a turning pocket, for example,is that the same lead edge of the sheet 2 continues to point intransport direction after said sheet has been turned over.

The belts 7, 8 are supported by the deflecting rollers 3, 4, 5 and 6. Inthis arrangement, the belt 7 is supported by an upper deflecting roller3 and by a lower deflecting roller 4. The belt segment 7′ carrying thesheet 2 moves between the underside of the deflecting roller 3 and theupper side of the deflecting roller 4, and the returning belt segment 7′moves from the underside of the deflecting roller 4 to the upper side ofthe deflecting roller 3. Correspondingly, the belt segment 8′ of thebelt 8 moves from the lower deflecting roller 5 on the top toward theupper deflecting roller 6 on the bottom, and the returning belt segment8′ of the belt 8 moves from the upper side of the deflecting roller 6 tothe lower side of the deflecting roller 5. To prevent the returning beltsegments 7′ and 8′ from rubbing against each other or against theadvancing belt segments 7′ and 8′, measures have to be taken. Forexample, this can be achieved by minimally inclining the position of thedeflecting rollers 3, 4, 5 and 6. To achieve the aforementioned purpose,it is also possible to use distancing rollers with collars.

Inasmuch as, referring to the described turning device 1, the turningsheet 2 must be held securely by the belt segments 7′ and 8′ and mustremained aligned while being turned over, it is suggested that at leastthree guide rollers 11, 12 and 13 be provided downstream of the crossingregion 10. These guide rollers 11, 12 and 13 are alternately arranged onthe belt segments 7′ and 8′ in such a manner that the belts 7 and 8 areminimally deflected out of the linear direction, so that the force withwhich these belt segments 7′ and 8′ act on the sheets 2 is increased,this requiring an inherent elasticity of the belts 7 and 8 that areused.

Inasmuch as the turning sheet 2 acts on the belts 7 and 8 withtransverse forces, it is suggested that at least one of the guiderollers 11, 12 and 13 be provided with at least one holding collar 14.Preferably, the guide rollers 11, 12 and 13 are arranged in such amanner that two guide rollers 11 and 13 are located in the upper regionand that a lower guide roller 12 is arranged between them. The secondupper guide roller 13 has a holding collar 14 in its rear region, i.e.,on side 15, on which the outer edge 16 of the sheet 2 is moved upwarddownstream of the crossing region 10. In this manner, it is ensured thatthe absolute positioning and the relative positions of the belt segments7′ and 8′ are maintained and, in so doing, also the positioning of therelatively thin sheet 2 is maintained.

FIG. 1 is a perspective view of the turning device. This shows how theturning of a sheet 2 in the direction of the arrows 17 takes place.During this process, at the beginning of the turning device 1, the rearedge 16′ moves up, i.e., toward the zenith, and the front outer edge 16is down in the crossing region 10. Then, the upper outer edge 16′ movesforward and down, and the lower outer edge 16 moves backward and up, sothat, at the end of the turning device 1, the formerly rear outer edge16′ is in front and the formerly front outer edge 16 is in back, inwhich case the descriptions “back” and “front” are with respect to theviewer of FIG. 1.

The turning operation is supported by guiding devices 19, 20 and 21. Oneguiding device 19 is used for guiding the edge 16′ of the sheet 2, saidguiding device 19 starting on side 15, at which the outer edge 16′ ofthe sheet 2 is moved upward, and then extending forward in such a mannerthat the outer edge 16′ is guided up to the end position of the sheet 2,when said sheet leaves the turning device 1. Only the course of theguiding device 19 has been drawn; for simplification, the mount of saiddevice has been omitted. It is essential that the guiding device 19 onside 15 extend far enough toward the back and be mounted in such amanner that the mount does not impair the turning of the sheet 2.

Another guiding device 20 is used to guide the outer edge 16 which ismoved upward downstream of the crossing region 10, until the sheet 2 hasreached the end position. In so doing, the edge 16, or the area of thesheet 2 adjoining the edge 16, slides upward on the guiding device 20,until said sheet has reached the horizontal plane.

The third guiding device 21 is used to support the edge 16′ toward theend of the turning operation, so that said edge is prevented fromhanging down. To achieve this, the guiding device 21 extends far enoughtoward the outside that it reaches up to the edge 16′. It is shown cutoff in FIG. 1 in order to not completely hide the lower deflectingroller 4.

The embodiment of FIG. 1 also shows that each of the deflecting rollers3, 4 and 6 is provided with two holding collars 14 in order to ensure asafe guiding of the belts 7, 8 which are configured as V-belts.

In a side elevation, FIG. 2 shows in a much more schematic and basicmanner an embodiment of an inventive turning device based on a turningdevice 1 as in FIG. 1. The turning device as in FIG. 2 is not true toscale and shown truncated in its longitudinal extension.

The turning device as in FIG. 2 comprises the deflecting rollers 3, 4, 5and 6, on which rotate the belts 7, 8 having belt segments 7′, 7″, 8′and 8′. In addition, in accordance with the invention, the belt segments7″, 8′ are guided over guide rollers 22, 23 and are essentiallydeflected approximately in an S-form. In so doing, the guide rollers 22,which can be moved in the directions of double arrows 24, are subject tothe spring bias of springs 25 in the outward pointing directions 26 ofthe double arrows 24. As a result of this, the belts 7, 8, which aremanufactured in accordance with the invention so as to displayessentially no inherent elasticity, are tightened in such a manner thatthe guiding belt segments 7′, 8′ abut against each other in a tautmanner, and securely clamp and transport, as well as turn over, a sheetlocated between them.

1. Turning device for transporting and turning over sheets of printingmaterial in a printing machine, preferably an electrophotographicprinting machine, said device comprising at least two belts, which, inparticular, consist essentially of a plastic material, each of saidbelts being deflected as closed loops over respectively at least twodeflecting elements and being crossed in order to turn over therespective sheet by approximately 180 degrees about its axis pointing intransport direction, in which process said sheet is held by clamping andfrictional engagement between abutting segments of the tensioned belt,characterized in that at least one of the belts is configured in anon-elastic manner, specifically reinforced, and that, in order totension this belt, a tensioning device is provided.
 2. Turning device asin claim 1, characterized in that the tensioning device comprises adeflecting element which deflects or bends the belt.
 3. Turning deviceas in claim 2, characterized in that the deflecting element is a roller.4. Turning device as in claim 2 or 3, characterized in that thedeflecting element is subject to a spring bias in tensioning direction.5. Turning device as in claim 2, 3 or 4, characterized in that the beltis deflected essentially in S-form over two deflecting elements in theregion of a tensioning device.